Embodiments relate generally to the field of marine geophysical surveying and, more particularly, embodiments relate to methods and systems for enabling anti-twist functionality in marine geophysical streamers.
Techniques for geophysical surveying include marine geophysical surveying, such as seismic surveying and electromagnetic surveying, in which geophysical data may be collected from below the Earth's surface. Geophysical surveying has applications in mineral and energy exploration and production to help identify locations of hydrocarbon-bearing formations. Certain types of marine geophysical surveying, such as seismic or electromagnetic surveying, may include towing an energy source at a selected depth—typically above the seafloor—in a body of water. One or more geophysical streamers also may be towed in the water at selected depths—typically above the seafloor—by the same or a different vessel. The streamers are typically cables that include a plurality of sensors disposed thereon at spaced apart locations along the length of the cable. Some geophysical surveys locate sensors on ocean bottom cables or nodes in addition to, or instead of, streamers. The sensors may be configured to generate a signal that is related to a parameter being measured by the sensor. At selected times, the energy source may be actuated to generate, for example, seismic or electromagnetic energy that travels downwardly into the subsurface rock. Energy that interacts with interfaces, generally at the boundaries between layers of rock formations, may be returned toward the surface and detected by the sensors on the streamers. The detected energy may be used to infer certain properties of the subsurface rock, such as structure, mineral composition and fluid content, thereby providing information useful in the recovery of hydrocarbons.
Some known streamers may be based on a dual strain member mechanical backbone. This implementation may be well suited for the in-line tension and reeling requirements of current systems. However, the dual strain member implementation typically has little torsion stiffness, which enables the streamer to rotate (almost) freely around its center axis (also referred to herein as “twist”). Other streamer designs (e.g., sensor stress member streamers) may also have little torsion stiffness also allowing streamer rotation. Such rotation may have severe mechanical and robustness consequences.
Devices used in the control of streamer orientation and/or position may include lateral force and depth (LFD) control devices, also referred to as “birds.” LFD control devices may be used for changing the orientation and/or position of the streamer. In one example, LFD control devices may include variable incidence wings that are rotatably fixed onto the streamer. While LFD control devices have been used in controlling the orientation and/or position of streamers, some LFD control devices have been observed to have non-optimal anti-twist functionality, leaving remnant twist in streamer sections. For example, FIG. 1 illustrates a streamer section 2 with a nearly 100° twist between adjacent spacers 4, which may be caused due to malfunction of a LFD control device.
Accordingly, there is a need for improved methods and systems for detecting and removing streamer twist.